The present invention relates to the field of communication in a downhole environment, particularly in a downhole network integrated into a drill string used in oil and gas exploration, or along the casings and other equipment used in oil and gas production. Gathering information of the actual operation of a drill string and the geological formations surrounding a well bore may assist drilling operations. Many systems have been disclosed which transmit information along a tool string, and these systems may be referred to in separate categories.
A first category includes references which employ direct electrical contacts between pipes. An example of such a system is U.S. Pat. No. 4,953,636 which is herein incorporated by reference for all that it discloses. The '636 patent discloses a pipe assembly for use in production or drilling systems. The pipe assembly comprises a plurality of pipe members connected together in end-to-end relationship and a plurality of tubular conductor members electrically connected together in end-to-end relationship. Other examples of such systems are disclosed in the following U.S. Pat. Nos. 6,296,066, 6,688,396; which are both incorporated by reference herein for all that they disclose.
A second category includes references which employ optical fibers and fiber optic couplers between pipes. An example of such a system is U.S. Pat. No. 6,734,805 which is herein incorporated by reference for all that it discloses. The '805 patent discloses a section of pipe for well operations which has a cylindrical fiber composite pipe body and a pair of metallic end fittings. Each pipe is also provided with an optical fiber for data transmission, and a fiber optic coupling is located at each end of the optical fiber for sending and receiving data transmissions via optical signals. Also disclosed is replacing the optical fiber with an electrical conductor, and the fiber optic coupling with electrical connectors and/or contacts.
A third category includes those references which employ inductive couplers between pipes. The term “inductive coupler” is herein intended to refer to a loop or loops of one or more wires and a path through the loop(s) through which inductive flux may flow. Generally an inductive coupler may transfer magnetic energy to another inductive coupler through mutual inductance between the two inductive couplers. The amount of magnetic energy transferred may be affected by the number of loops, the number of wires, magnetic permeability of material in the path through the loops, or proximity and orientation of one coupler to another. An example of a system which employs inductive couplers is U.S. Pat. No. 6,641,434 which is herein incorporated by reference for all that it discloses. The '434 patent discloses a wired pipe joint including a first annular coil fixedly mounted to a box-end, and a second annular coil fixedly mounted to a pin-end. The '434 patent also discloses a redundant system of two pairs (or more) of wires which could be run from end to end on each joint and two independent coil windings could be wound in each coupler, so that a single broken wire would not cause a system failure. Other examples of such systems are disclosed in the following U.S. Pat. No. 6,670,880 ('880 patent) and U.S. Pat. No. 6,866,306 which are herein incorporated by reference for all that they disclose.